1. Field of the Invention
This invention relates to wireless communication systems, and in particular to directional antennas for use in wireless communication systems.
2. Background
In wireless communication systems, antennas are used to transmit and receive radio frequency signals. In general, the antennas can be omni-directional, receiving and transmitting signals from any direction, or directional, with reception and transmission of signals limited in direction. In general, directional antennas provided increased gain over an omni-directional antenna because the directional antenna's coverage is focused over a small spatial region. Because a directional antenna covers a limited spatial region, the antenna needs to be “pointed” so that it can transmit and receive signals in a desired direction. Some conventional antenna systems include multiple directional antennas, or elements, arranged in an array such that individual elements “point” in different directions. By selecting desired elements of the array the overall direction of the antenna system can be varied. In addition, there exist antenna systems which provide directive gain with electronic scanning, such as phased arrays, rather than being fixed. However, many such electronic scanning technologies are plagued with excessive loss and high cost. In addition, many of today's wireless communication systems provide very little room for antennae elements.
Conventional directional antennas include the traditional Yagi-Uda (“Yagi”) antenna, as well as phased arrays. A traditional Yagi antenna includes a driven element, the element a signal is fed to by a transmitter or other signal source, called the driver or antenna element, one or more reflectors, and one or more director elements. In conventional Yagi antennas, the spacing between the elements is critical and varies from one design to another, with element spacing typically varying between one-eighth and one-quarter wavelength. While the Yagi antenna does provide a relatively simple directional antenna design, the overall size is usually relatively large because of the reflector and director elements and the spacing between the elements.
A phased array typically includes multiple antennas that are driven with signals that have had their relative phase varied such that the signals radiated from the multiple antennas combine constructively in a desired direction and destructively in other directions. Adjusting the relative phase of the signals feeding the multiple antennas requires complicated electronic circuitry.
There is a need in the art for improved antennas that can provide directional gain, are simple, and are compact in size.